Why Lambda Needs an Explicit DependsOn on S3 in CloudFormation
This DVA-C02 practice question tests your understanding of development with aws services. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
Exhibit
Refer to the exhibit.
Consider the following CloudFormation template snippet:
Resources:
MyBucket:
Type: AWS::S3::Bucket
Properties:
BucketName: my-unique-bucket-12345
VersioningConfiguration:
Status: Enabled
MyLambdaFunction:
Type: AWS::Lambda::Function
Properties:
Handler: index.handler
Role: !GetAtt LambdaExecutionRole.Arn
Code:
S3Bucket: !Ref MyBucket
S3Key: function.zip
Runtime: nodejs18.x
A developer is reviewing a CloudFormation template that creates an S3 bucket and a Lambda function. The Lambda function's code is stored in the S3 bucket. What is a potential issue with this template?
Exhibit
Refer to the exhibit.
Consider the following CloudFormation template snippet:
Resources:
MyBucket:
Type: AWS::S3::Bucket
Properties:
BucketName: my-unique-bucket-12345
VersioningConfiguration:
Status: Enabled
MyLambdaFunction:
Type: AWS::Lambda::Function
Properties:
Handler: index.handler
Role: !GetAtt LambdaExecutionRole.Arn
Code:
S3Bucket: !Ref MyBucket
S3Key: function.zip
Runtime: nodejs18.x
A
The Lambda function's role is referenced incorrectly; it should be 'Ref' instead of 'GetAtt'.
Why wrong: GetAtt is used to get the Arn attribute.
B
The Lambda function depends on the S3 bucket, but there is no DependsOn clause to ensure the bucket is created first.
CloudFormation may attempt to create the Lambda function before the bucket exists, causing failure.
C
The bucket name 'my-unique-bucket-12345' is not globally unique.
Why wrong: The bucket name appears unique, but the main issue is dependency.
D
The bucket must have versioning enabled to store Lambda code.
Why wrong: Versioning is not required for storing Lambda code.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The Lambda function depends on the S3 bucket, but there is no DependsOn clause to ensure the bucket is created first.
The Lambda function's code is stored in the S3 bucket, so the bucket must exist before the Lambda function can be created. Without an explicit DependsOn clause, CloudFormation may attempt to create the Lambda function before the S3 bucket, causing a failure because the Lambda function references a bucket that does not yet exist. CloudFormation does not automatically infer dependencies from resource references in properties like `Code.S3Bucket`; you must declare them explicitly.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
The Lambda function's role is referenced incorrectly; it should be 'Ref' instead of 'GetAtt'.
Why it's wrong here
GetAtt is used to get the Arn attribute.
✓
The Lambda function depends on the S3 bucket, but there is no DependsOn clause to ensure the bucket is created first.
Why this is correct
CloudFormation may attempt to create the Lambda function before the bucket exists, causing failure.
Related concept
Read the scenario before looking for a memorised answer.
✗
The bucket name 'my-unique-bucket-12345' is not globally unique.
Why it's wrong here
The bucket name appears unique, but the main issue is dependency.
✗
The bucket must have versioning enabled to store Lambda code.
Why it's wrong here
Versioning is not required for storing Lambda code.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume CloudFormation automatically orders resource creation based on any reference in the template, but it only does so for intrinsic function references (Ref/GetAtt), not for string literals like bucket names.
Detailed technical explanation
How to think about this question
CloudFormation's resource dependency resolution is based on `Ref` and `Fn::GetAtt` intrinsic functions; if a resource property references another resource via these functions, CloudFormation automatically adds a dependency. However, the `Code.S3Bucket` property in a Lambda function uses a string literal (not an intrinsic function), so CloudFormation cannot infer the dependency. In real-world scenarios, this can cause intermittent deployment failures, especially when the bucket is created in the same stack and the Lambda function is created before the bucket finishes provisioning.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.
Quick reference
AWS S3 Storage Class Comparison
Storage Class
Min Duration
Retrieval
Use Case
S3 Standard
None
Immediate
Frequently accessed data
S3 Standard-IA
30 days
Immediate
Infrequent access, rapid retrieval
S3 One Zone-IA
30 days
Immediate
Non-critical infrequent data
S3 Intelligent-Tiering
None
Immediate–hours
Unknown or changing access patterns
S3 Glacier Instant
90 days
Milliseconds
Archive with instant retrieval
S3 Glacier Flexible
90 days
Minutes–hours
Archive, flexible retrieval
S3 Glacier Deep Archive
180 days
Hours
Long-term compliance archive
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Development with AWS Services — This question tests Development with AWS Services — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The Lambda function depends on the S3 bucket, but there is no DependsOn clause to ensure the bucket is created first. — The Lambda function's code is stored in the S3 bucket, so the bucket must exist before the Lambda function can be created. Without an explicit DependsOn clause, CloudFormation may attempt to create the Lambda function before the S3 bucket, causing a failure because the Lambda function references a bucket that does not yet exist. CloudFormation does not automatically infer dependencies from resource references in properties like `Code.S3Bucket`; you must declare them explicitly.
What should I do if I get this DVA-C02 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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